What Prompted Early Scientists to Propose That the Ray of the Cathode

What prompted early scientists to propose that the ray of the cathode ray tube was due to the cathode?

A) The ray was present regardless of gas, or even without a gas.
B) The ray was attracted to positively charge electric plates.
C) The ray was not seen from the positively charged anode.
D) The ray could be diverted by a magnetic field.
E) The ray would change colors depending on which gas was used inside the tube.